1. Field of the Invention
The present invention relates to a molding die, and more specifically to a glass molding die and renewal method thereof.
2. Description of the Related Art
A molding die disclosed in JP2003-277074 by Yokoyama et al. sequentially provides a chromium layer and platinum-iridium alloy layer, or a chromium layer, a chromium nitride layer, and platinum-iridium alloy layer overlying a tungsten carbide substrate. The chromium layer is hard chromium, having high hardness and wear resistance. The ground molding die can maintain good surface accuracy (low peak to valley value) and low roughness resulting from the wear of the platinum-iridium alloy layer during predetermined time being as five times as that of the chromium layer, accelerating renewal thereof. When the surface profile of the chromium layer deviates, however, the chromium layer quickly can damage a diamond tool because chromium is a transition element, having unshared electrons in d orbital with resulting chemical wear to the diamond tool. When correcting the surface profile of the chromium layer using grinding, the renewing process is difficult and time-consuming resulting from the high wear resistance of the chromium layer.